Up Close at Alpha Centauri

byPaul GilsteronDecember 6, 2016

In early December the Harvard-Smithsonian Center for Astrophysics offered as part of its fall colloquium series a talk by Harvard’s Avi Loeb, fortunately captured on YouTube as Project Starshot: Visiting the Nearest Star Within Our Lifetime. We’ve looked at Breakthrough Starshot in many posts on Centauri Dreams, including my reports from the last set of meetings in Palo Alto, but for those new to the concept of using a laser array to send small, instrumented sails to the Alpha Centauri stars, this video is a fine introduction.

You’ll recall that yesterday I talked about Robert Austin’s futuristic Asteroid Belt Astronomical Telescope, with an illustration of what such an instrument might see of the exoplanet Gliese 832c. If Starshot can achieve its goals, it will be able to make out continent sized features on the surface of Proxima b, or perhaps a planet around Centauri A or B. It would achieve, in other words, what it would take a near-Earth space-based telescope 300 kilometers wide to equal.

Image: What we can see today. The NASA/ESA Hubble Space Telescope has given us this stunning view of the bright Alpha Centauri A (on the left) and Alpha Centauri B (on the right), shining like huge cosmic headlamps in the dark. The image was captured by the Wide-Field and Planetary Camera 2 (WFPC2). WFPC2 was Hubble’s most used instrument for the first 13 years of the space telescope’s life, being replaced in 2009 by Wide-Field Camera 3 (WFC3) during Servicing Mission 4. This portrait of Alpha Centauri was produced by observations carried out at optical and near-infrared wavelengths. Credit: ESA/NASA.

Starshot envisions sending swarms of sails to its target stars, each moving at 20 percent of the speed of light. Each four-meter square lightsail would itself be used as the transmitter dish to beam data back to Earth showing us images of the planet, with each sail sending 100 images over the course of its observations. The time frames are interesting: If all goes without a hitch (and it’s hard to conceive of there being no hitches in a plan this ambitious), it will take several decades to build a beamer and create the actual sails and payload.

Then we have a launch, which takes place in a timeframe of minutes, as a mothership in a highly elliptical orbit releases a sail that is then under the beam for an intense 60,000 g ride. You can imagine all the stresses this puts on the sail, and again, we’ve talked about most of these in previous posts, but Avi Loeb’s presentation offers an excellent refresher, covering factors like sail stability under the beam, sail materials and interstellar dust encounters.

The launch phase ends in minutes and a 20 year cruise phase begins. In the Proxima Centauri system after the journey, each sail now faces an encounter time measured in hours. Thus the pattern: Hurry up and wait. For after the flyby, we face more time, a 4.24 year wait for the first images of the planet to come back to Earth. Interestingly, despite moving at relativistic speed, the planet’s image will remain circular thanks to so-called Terrell rotation.

Loeb mentions as a driver for investigation of Proxima Centauri in particular the fact that M-dwarfs make up a huge percentage of all the stars in the galaxy, and they can live for trillions of years. If we learn that life exists around this kind of star, we learn that living things will have incredibly long timeframes to continue to evolve. We also learn that the kind of environments found around red dwarfs are far more common than what we find around our own familiar G-class star. In many respects, we may wind up being the outliers.

Facets of the Journey

Yesterday I asked what effect being able to see images of planets like Proxima b from telescopes in our own Solar System would have on our thinking. Some would argue that we’ll reach the point where we can learn enough about exoplanets in such observations and will not need to build probes to other stars. My own view is that the two prospects work together. I think any images of a living, Earth-like world around a nearby star are going to focus interest in getting a payload into that system in order to make close up imagery and data possible.

On that score, you’ll recall Project Blue, the attempt to build a small space telescope explicitly designed to detect possible planets in the habitable zones around Centauri A and B (see Project Blue: Imaging Alpha Centauri Planets). Documentary filmmakers who are supporting Project Blue bring Debra Fischer (Yale University), one of its key players, into their new short video Traveling to Alpha Centauri? which explores the same terrain.

Although the video suggests antimatter rather than laser-beamed sails as a solution to the propulsion problem, Fischer’s comments go to the question of what the information we gain from our telescopes can motivate us to do.

If we discover an Earth-like planet orbiting Alpha Centauri, this is really going to drive a whole new era in science, an explosion, to finally go out into the galaxy and to start exploring other worlds.

Fischer goes on to speak of a ‘new wave within humanity to begin taking our steps out of our Solar System’ as a part of achieving the destiny of our species. I’m in agreement, and not just at the level of Project Blue. We could know within a decade or so about possible planets in the habitable zones of the two primary Centauri stars, and we may be able not long afterward to begin analyzing their atmospheres. I believe that hints of life on such worlds will ignite the imagination of the general public in support of projects to explore them up close. To me, Breakthrough Starshot and Project Blue, so different in their scale and conception, are nonetheless two sides of the same coin. An exploring species watches, learns and goes.

Comments on this entry are closed.

Micky BadgeroDecember 6, 2016, 15:54

That is diffusion, diffraction and saturation of the sensor pixels, right? Not disk images and coronas?

Thanks for the correction and the list of resolved stars. I was surprised to see that Proxima was even on that list (by the VLT). But Hubble couldn’t resolve the AC stars, so Micky’s assumption was correct. :)

I believe none of these are actual images. To resolve stars, you need to use interferometry, which is somewhat different from imaging. AFAIK, the image is computed, not directly projected onto a sensor array.

The true cost of the completion of Breakthrough Starshot has not been determined. How much will the lasers to push the sail cost? Until we get better interstellar travel technology that has a better success rate I think money is better spent on a space telescope than can image exoplanets with full spectroscopic capabilities.

Lets image Proxima B before we send anything there to see if it is worth the trip.

Proxima Centauri, and by proxy of being part of it, Alpha Centauri are the closest suns to our own Sol system, barring some rogue brown dwarf or exoworld. We will be sending probes to them first whether they have “interesting” planets or not, however you may be defining an actual alien world as interesting.

I hope our culture hasn’t become that blaze about something real, alien, and extraordinary as a distant planet will be, even if there are thousands that we know of, hundreds of billions that we suspect exist in the Milky Way galaxy alone, and are envisioned by numerous science fiction stories and video games all the time. Anyone who recalls or studies the Voyager probe missions to the outer Jovian planets and their moons knows just how well reality can outdo human imaginations and expectations.

Many considered the Viking Mars landers of 1976 to be ultimately failures because they did not give clear indications that they had detected life on the Red Planet. These critics completely missed all the incredible successes the two robot explorers did accomplish, especially being the first truly successful landers on Mars in history!

Yes, the Soviet Mars 3 probe did make it to the surface intact in late 1971, but its signal was lost 90 seconds after landing and Mars 3 only transmitted part of an image where nothing could really be made out.

The other problem with the Viking mission is that the folks who conceived and built it had preconceived notions about what life on Mars would be like and how it would be found. That and several centuries of inflated hopes about Martian life – which remained to a degree even after the revelations of Mariner 4 and to a continued extent Mariner 6 and 7, only to be reinflated by the revelations of the Mariner 9 orbiter – led to a general disappointment and confusion, causing there to be no further American landing attempts at Mars until almost two decades later.

And all that being said, now that NASA has confirmed multiple times that the Red Planet once had lots of water and there is still a lot of it encased in subsurface ice fields, they need to get really serious about find native organisms:

Shouldn’t we be looking at building an incrementally expansive space telescope? Instead of these current one-offs?

Say, start with two pieces: A free flying imaging system, and a free flying mirror segment. Use a nice, really long focal length, so that you have room for plenty of them. Then you can just keep adding mirrors.

With a large focal length like that, it would be possible to use more than one imaging system at the same time. So both ends of the system could be incrementally improved.

“If we discover an Earth-like planet orbiting Alpha Centauri…” If aliens on a planet around Alpha Centauri have telescopes similar to ours that can detect exoplanets via stellar wobble or planetary transit, how many of our sun’s planets could they detect in the same amount of time we’ve been looking at the Centauri system? To the best of my knowledge we’ve detected one planet around Proxima Centauri and maybe one around Alpha Centauri B. So are our current telescopes inadequate, or have we likely found all the planets in that system?

> So are our current telescopes inadequate, or have we likely found all the planets in that system?

We have barely even begun to search Alpha Centauri for planets. To date, surveys using a variety of techniques have only eliminated the possibility of Saturn to Jupiter-size gas giants orbiting either Alpha Centauri A or B inside about 2 AU (corresponding roughly to the outer limit of a stable orbit around either star). Direct imaging results also seem to exclude objects larger than small to moderate-size brown dwarfs orbiting around Alpha Centauri AB from 300 AU to about 50 AU (corresponding roughly to the inner limit of a stable P-type orbit around α Centauri AB).

The detection of Alpha Centauri Bb in 2012 is now widely regarded as being spurious with natural noise irregularly sampled in time being mistaken for the radial velocity signature of an orbiting planet. However, there was a transit-like event observed by Hubble which *MIGHT* indicate the presence of an Earth-size planet in a close orbit:

While we may be reaching the practical limits of what precision radial velocity measurements may reveal about any planets that might orbit Alpha Centauri A or B (or even the barycenter of AB), we do have the technology to detect Earth-twins in the habitable zones of these stars using a fairly modest-size space telescope. Like I said, we have barely begun the search for planets.

We better get used to dealing with multiple star systems in terms of interstellar navigation and related issues because over half the stars in the Milky Way galaxy are part of multiple systems. We also now know that exoplanets in such systems are also stable over long time periods, so they will also make more suitable scientific targets, especially searching for life signs.

I am pretty sure none of our planets would be detected from Alpha Centauri with the methods we have now. None. Even Kepler would not be able to detect any of our planets, had our sun been in its field with our planets edge on. That is how bad our current methods are.

Below is an abstract for a talk on planets in close binary systems to be given at the next meeting of the American Astronomical Society (the 229th).

CONTROL ID: 2623770
SUBMISSION ROLE: Research Contributed or Dissertation
DATE/TIME CREATED: October 4, 2016, 4:09 PM
TITLE: The Ruinous Influence of Close Binary Companions on Planetary Systems
ABSTRACT BODY:
Abstract (2,250 Maximum Characters): The majority of solar-type stars are found in binary systems, and the dynamical influence of binary companions is expected to profoundly influence planetary systems. However, the difficulty of identifying planets in binary systems has left the magnitude of this effect uncertain; despite numerous theoretical hurdles to their formation and survival, at least some binary systems clearly host planets. We present high-resolution imaging of nearly 500 Kepler Objects of Interest (KOIs) obtained using adaptive-optics imaging and nonredundant aperture-mask interferometry on the Keck II telescope. We super-resolve some binary systems to projected separations of under 5 AU, showing that planets might form in these dynamically active environments. However, the full distribution of projected separations for our planet-host sample more broadly reveals a deep paucity of binary companions at solar-system scales. When the binary population is parametrized with a semimajor axis cutoff a cut and a suppression factor inside that cutoff S bin, we find with correlated uncertainties that inside acut = 47 +59/-23 AU, the planet occurrence rate in binary systems is only Sbin = 0.34 +0.14/-0.15 times that of wider binaries or single stars. Our results demonstrate that a fifth of all solar-type stars in the Milky Way are disallowed from hosting planetary systems due to the influence of a binary companion.

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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